The meteorite ALH
84001, where possible traces of martian life have been found, is one of
the oldest rocks ever studied, and probably came from the oldest regions
on Mars. These ancient parts of Mars, most of its southern hemisphere,
are covered with asteroid impact craters, like this area in the bright
region of Noachis. This part of Mars is as cratered as the Moon’s
highlands, and so is about the same age, more than 4 billion years old.

The biggest crater
here is Proctor, named for a nineteenth-century British astronomer. The
dark splotches inside Proctor and many other craters are fields of sand
dunes. In high-resolution images, these linear dunes look like waves on
the ocean, but actually show how dry and desolate Mars is now.